Effects of the LBV Primary Star's Mass Loss Rate on Eta Carinae's Spatially-Extended, Time-Variable Massive Binary Colliding Winds

At the heart of Eta Carinae's spectacular bipolar ``Homunculus" nebula lies an extremely luminous (5 × 10^6 Lo) colliding wind binary with a highly eccentric (e ~ 0.9), 5.54-year orbit and a total mass ≥ 110 Mo. Our closest (D ~ 2.3 kpc) and best example of a pre-hypernova or pre-gamma ray burst environment, Eta Carinae is an ideal astrophysical laboratory for studying massive binary interactions, stellar wind-wind collisions, and massive star evolution. Over the past fifteen years, the central source has brightened by one stellar magnitude in the optical. Changes in P Cygni wind profiles such as Hα have also been observed. Extended X-ray monitoring and spectroscopy further indicate that the hydrogen column density in line of sight dropped two-fold by the 2009 periastron event. A simple interpretation for the cause of these changes is a factor of two drop in the mass-loss rate of the LBV primary star over the last decade and a half. However, 1D CMFGEN radiative transfer models predict that such a large change in the primary mass-loss rate would lead to huge changes in the observed stellar spectrum. In an effort to further investigate the effects that a change in the mass-loss rate of the primary would have on the system, we performed large- (±1620 au) and small- (±162 au) scale full 3D smoothed particle hydrodynamic (SPH) simulations of Eta Car's binary colliding winds assuming three different mass-loss rates for the LBV primary. Results from these new 3D simulations (which include optically-thin radiative cooling and radiation-driven stellar winds) combined with various multi-dimensional radiative transfer codes indicate that a factor of two change in the mass-loss rate of the primary should lead to significant changes in various X-ray, UV, Optical, and near-IR diagnostics. We discuss what changes are expected and why, and offer some possible explanations for the recent changes observed in Eta Car. We also discuss the importance of constraining this likely supernova progenitor's recent mass loss history.status: publishe